Conventionally, the discrimination and evaluation of odors is performed by the olfactory sense of human beings. By this method, it must be considered that different persons (or panels) have different olfactory sensitivities and the olfactory sense of a panel may change depending on the physical condition on the day of the test. Therefore, to obtain an objective result with high accuracy, it is necessary to gather an adequate number of panels and to conduct the test under an adequately uniform environmental condition. Thus, the test often consumes a lot of time and labor. Further, even under a desirable physical and environmental condition, it is very difficult to obtain a conclusive result based on a fixed standard because the olfactory sense of the human being easily adapts to odors.
In view of such problems, some conventional methods use a gas chromatograph (GC) or a gas chromatograph/mass spectrometer (GC/MS) to analyze and discriminate the components of the odor concerned. These methods treat the odor as a volatile chemical substance and can effectively identify the causative agent of the odor. However, the conventional methods cannot correlate the odor composition with the organoleptic evaluation by the olfactory sense of the human being.
A conventional device that is designed to make up for the aforementioned problem is a product of Gerstel (http://www.gerstelus.com), called the “Olfactory Detector Port (ODP-2).” ODP-2, which is an attachment for a gas chromatograph, allows a panel to smell the effluent sample separated by the column of the gas chromatograph and enter information about the odor intensity in real-time while the sample is being analyzed with the detector. The information entered by the panel is used to create a graph showing the change of the odor intensity with time. The relation between the chromatogram created by the gas chromatograph and the aforementioned graph enables the analysis on the relation between the odor composition and the organoleptic evaluation. The aforementioned device, however, has a problem in that it requires the panel to continue smelling the odor for a relatively long period of time (for example, one hour). Concentrating on the smelling of the odor for such a long time not only imposes a burden on the panel but also causes the adaptation of the olfactory sense to the odor, as explained previously. Furthermore, the method cannot be used if the odor contains a harmful substance.
A group including an inventor of the present invention has developed an odor discriminating apparatus using odor sensors responsive to odorous substances, as disclosed in the Japanese Unexamined Patent Publication No. 2003-315298 and on the following website: http://www.an.shimadzu.co.jp/products/food/ffl.htm. The apparatus includes plural pieces of odor sensors having different response characteristics and calculates the quality and intensity of an odor by processing the detection signals of the odor sensors by a cluster analysis, a principal component analysis or other types of multivariate analysis, or by a non-linear analysis using neural networks. This type of odor discriminating apparatus treats an odor as a mixed odor and does not separate it into components, enabling the comparison and determination of mixed odors or the calculation of an odor index or other index indicating the odor intensity in terms of the olfactory sense of the human being. This apparatus, however, sometimes fails to detect a very small quantity of an odor component accompanied by a large quantity of another odor component.
Recently, the growing awareness of environmental issues has increased the necessity for odor measurements, and the measurement should now cover a wider variety of odors that have very complex compositions. However, none of the above-described conventional methods can satisfy this requirement. They reflect only a limited aspect of the odor, which may lead to a misunderstanding of the measurement result in some cases. Furthermore, since the measurement result is devoid of objectivity, it is often difficult to compare plural sets of measurement results obtained at different spots and/or different points in time. Another problem is that the measurement efficiency is hard to improve. In view of such problems, the main object of the present invention is to provide an odor measuring apparatus capable of efficiently measuring a mixed odor having a complex composition with a high level of objectivity.